The present invention relates to a bottom hole well pump and more specifically to such a pump including a linear action motor for producing reciprocating action of a plunger in one or more pumping chambers.
A number of different types of bottom hole well pumps have been provided in the prior art for raising oil or other liquids from substantial depths underground. Most commonly, the pump assembly may be suspended at a suitable pumping depth in the well while being mechanically operated by a reciprocating sucker rod extending to the surface of the well. Such pumps are generally inefficient, particularly in deep wells because of the need for the reciprocating sucker rod to extend from the surface toward the bottom of the well. At the same time, such pumps have suffered because of the likelihood of mechanical separation along the entire length of the sucker rod.
Accordingly, the prior art has also provided a variety of bottom hole pumps which avoid the need for a mechanically reciprocating rod extending throughout the entire depth of the well. Rather, these pumps include electrically actuated pumping means such as a linear motor interconnected by an electrical conduit with a power source and control means at the surface of the well. Such pumps have been found to be generally efficient and may employ a linear motor in the form of either a solenoid motor, a DC motor or a stepper motor, for example. Pump assemblies of this type have been commonly employed in oil wells which are the major application for this type of pump. A number of different types of electrically operated pumps have been provided particularly for oil wells, as exemplified for example by U.S. Pat. No. 1,287,078, issued Dec. 10, 1918; U.S. Pat. No. 1,655,825, issued Jan. 10, 1928; U.S. Pat. No. 1,840,994, issued Jan. 12, 1932; U.S. Pat. No. 2,222,823, issued Nov. 26, 1940; and U.S. Pat. No. 3,031,970, issued May 1, 1962.
Although electrically operated pump assemblies of this type have been available for many years as indicated by the above patents, the importance of maintaining efficiency and continuity of operation in the pump has become even more important with the greater depth to which such wells must extend at present. Because of the greater depths, it is, of course, more time-consuming and costly in order to raise the pump assembly for making any necessary repairs and for reintroducing it at a suitable pumping depth within the well.
In addition to modern oil wells extending to greater depth, it has also become more common to place in commercial production wells which are of more marginal value. In such wells, the oil may seep into the well at diminishing rates during operation of the well. Accordingly, it may often be necessary during operation of the well to adjust performance of the pump in order to adapt it will the production capabilities of the well.
For these reasons, there has been found to remain a need for an efficient bottom hole pump which may be readily introduced even at great depths into wells of a type including a casing with a tubing of substantially smaller diameter than the casing and extending downwardly therethrough to a depth at which liquid is to be pumped from the well.